The applicant has already proposed actuator constant-volume ejection mechanisms of the aforementioned type, that is, actuator constant-volume ejection mechanisms of a type in which content of a container body is first flowed into and stored in a constant-volume chamber in a state where a constant-volume chamber outflow valve is closed as a result of constant-volume ejecting operation and the constant-volume chamber outflow valve is opened to eject the content of the constant-volume chamber into an external space subsequently (refer to Patent Documents 1 and 2).
As depicted in FIG. 6, the actuator constant-volume ejection mechanism of Patent Document 1 includes constituent elements, such as:                a stem 21;        a valve seat portion 22 (which corresponds to a valve member of this invention) attached to the stem 21;        an operating button body 25 (which corresponds to a pressing member of this invention) disposed movably up and down with respect to a single-structured member including the stem 21 and the valve seat portion 22; and        an operating button coil spring 23 provided between the valve seat portion 22 and the operating button body 25 for biasing the operating button body in an upward direction.        
Then, an annular valve seat 24 of the valve seat portion 22 and an annular valve element 26 of the operating button body 25 together constitute a constant-volume chamber outflow valve.
In stationary mode in which the operating button, body 25 is not depressed, the constant-volume chamber outflow valve is kept open by an elastic force of the operating button coil spring 23.
Needless to say, a constant-volume chamber inflow valve (=a valve made up of a stem peripheral surface hole for passing the content and a conventionally known stem gasket for opening and closing the stem peripheral surface hole) of the stem 21 is closed by action of a conventionally known coil spring for the stem at this time.
Meanwhile, the coil spring for the stem and the stem gasket which are conventionally known are similar to a stem coil spring 10 and a stem gasket 11 of FIGS. 1 to 5.
When the operating button body 25 is depressed from a stationary mode position thereof, only the relevant button body first descends, overwhelming the elastic force of the operating button coil spring 23, whereby the constant-volume chamber outflow valve is closed.
After the constant-volume chamber outflow valve has closed, the stem 21, the valve seat portion 22 and the operating button body 25 forming a single structure, that is, with the constant-volume chamber outflow valve closed, descends and, then, the constant-volume chamber inflow valve opens so that the content of the container body flows into the constant-volume chamber for storage therein.
When a user stops depressing an operating button, the stem 21 ascends due to elastic action of the coil spring for the stem, thereby closing the constant-volume chamber inflow valve, and the operating button body 25 ascends (relative to the valve seat portion 22) due to elastic action of the operating button coil spring 23, thereby opening the constant-volume chamber outflow valve. Therefore, the only content of the constant-volume chamber is ejected into the external space.
After further studying and examining the above-described actuator constant-volume ejection mechanism and producing evaluation sets thereof, the applicant has verified that even if the operating button coil spring for biasing the operating button body is eliminated, the output valve or the constant-volume chamber is brought to an “open” state by a pressure of liquefied gas or soluble compressed gas within the constant-volume chamber, or the content of the constant-volume chamber is ejected into the external, space is a reliable fashion.
The actuator constant-volume ejection mechanism of Patent Document 2 which is based on the aforementioned verification is an actuator constant-volume ejection mechanism of a type configured by eliminating the operating button coil spring 23.